Hand-held extruding apparatus

ABSTRACT

A hand-held extruding apparatus for applying thermoplastic sealant materials. The apparatus includes a barrel having a material feed passage extending therethrough. A plurality of heating element passageways extend parallel to the feed passage, with rod-like heating elements being mounted therein. A heat sensor is mounted in another parallel passageway in the barrel, and the sensor together with the heating elements are disposed in a control circuit enabling a preselected temperature to be accurately maintained. Material fed into the barrel is advanced by a motor-driven conveying screw toward an orifice at the outlet of the feed passage. The barrel is secured to a pistol-grip and housing portion of the device in such manner as to enable interchangeability of barrels, and to minimize heat transfer from the barrel to the grip and housing.

United States Patent [1 1.

Wolfrom Aug. 7, 1973 HAND-HELD EXTRUDING APPARATUS Primary Examiner-Robert B. Reeves [75] lnventor: Norman S. Wolfrom, Cranford, Assmam Emmmer Lans NJ. Attorney-Stefan JrKlauber 57 ABSTRA T I73| Assigneez Hardman Incorporated, Belleville, 1 v I C NJ, A hand-held extrudingapparatus for applying thermoplastic sealant materials. The apparatus includes a bar- [22] 8- 1972 rel having a material feed passage extending there- [21] App]. NO; 283,203 through. A plurality of heating element-passageways extend parallel to the feedpassage, with rod-like heating elements being mounted therein. A heat sensor is 1 325 fj ig g mounted in another parallel passageway in the barrel, 51 I t Cl v Bd and the sensor together with the heating elements are d 146 disposed in a control circuit enabling a preselected 1 3 3 219 temperature to be accurately maintained. Material fed I into the barrel is advanced by a motor-driven conveying screw toward an orifice at the outlet of the feed pas- [56] References cued sage. The barrel is secured to a pistol-gripand housing UNITED STATES PATENTS portion of the device in such manner as to enable inter- 3,337,093 8/1967 Newton 222/l46 HE changeability of barrels, and to minimize heat transfer Davis 219/302 X from the barrel to the grip and housing.

Miler 425/378 16 Claims, 15 Drawing Figures PAIENTED A118 7 I975 sazaiaura FIG.5

FIG. 3

PATENIED 3.750.905

SHEET 3 BF 4 FIG. 6

PAIENIED AUG 7 I975 SHEET '4 [IF 4 FIG. 10

HEATING LOA D 1 HAND-HELD 'EX'TRUDING APPARATUS BACKGROUND OF INVENTION This invention relates generally to extruding apparams, and more particularly relates to hand-held apparatus adapted for extruding materials displaying thermoplastic properties.

So-called polymeric sealant materials are thermoplastic rubber-based compositions which have come into increasing use for sealant applications, as for example where it is desired to effect a seal between the glass windshield and mating frame of an automobile. Such compositions may, for example, comprise polymerized butyl-based compounds; or may be based on polysulfide polymers, on styrene-butadiene rubber polymers, on acrylonitrile-butadiene rubber polymers, on other butyl rubbers, on neoprene, urethanes, or on combinations of these several components, and/or of other synthetic rubber-based materials.

In the course of using such materials, the basic objective sought to be achieved by the artisan is to lay down a bead of the sealant in a prescribed pattern upon one 1 of the surfaces'to be joined. The said material is commercially furnished in rope-like form,and in order to provide the desired well-defined bead, apparatus have from time to time been proposed which in one manner or another, extrude the sealant material under operator control. As the sealant material is thermoplastic in nature, a superior bead is deposited if the material-is first heated so that the extrudate may wet the surface upon which it is deposited and otherwise adhere firmly thereto. For such reason it has also been proposed in certain of the aforementioned prior apparatus, that heating be provided during the process ofextrusion.

While such prior devices as have been alluded to above have achieved a degree of commercial use, they have nevertheless in practice been found to be markedly ineffective and unreliable. A variety of causes may be cited in explanation of the failure of these devices to satisfy commercial requiremnts. Among such deficiencies has been the failure of these prior devices to provide sufficiently controlled and uniform heating of the extrudate, in consequence of which the product provided washighly irregular, lacking in uniformity, and poorly adherent. In many instances, furthermore, the configuration utilized to achieve heating is such as to introduce inordinate heating into parts of the apparatus engaged by the operator, with consequent discomfort and hazard to such operator.

the prior material is eliminated with consequent and obvious waste.

In accordance with the foregoing, it may be regarded as an object of the present invention to provide a handheld extruding apparatus for applying thermoplastic sealant materials, which is readily held and actuated by an operator, and which is provided with means enabling accurate and uniform heat control of the extrudate.

I 7 It is a further object of the present invention to provide hand-held apparatus for extruding thermoplastic sealant materials, which includes efficient variable speed means for feeding the said materials, which provides for uniform and highly regulated heating of the extrudate, and which moreover minimizes heating and electrical hazards to an operator.

It is yet a further object-of the present invention to provide a hand-held extruding apparatus for thermoplastic sealant materials, which provides readily interchangeable barrel portions, whereby an operator may readily change the apparatus configuration for extru sion of successive types of differing materials, thereby avoiding contamination.

SUMMARY OF INVENTION Now, in accordance with the present invention, the foregoing objects and others as will become apparent in the course of the ensuing specification are achieved in a hand-held apparatus including a barrel having a material feed passage extending therethrough and a plurality of heating element passageways extending parallel to the feed passage. A feed screw is mounted for rotation in the feed passage with motor means being secured to one end of the barrel block, and actuated by a trigger .on a pistol grip associated with the said motor means. The barrel block has a plurality of heating element passageways extending parallel to the feed passage and rod-like heating elements, such as cal-rods," extend in the said passageways for a substantial part of the :length of the feed passage. A heat sensor, such as a thermistor, is mounted in the barrel block for sensing curately maintain a preselected temperatureat the bar- 'Such apparatus as are currently available for the ,pur-

poses cited above, also are relatively unsatisfactory withrespect to the feed mechanisms utilized for the sealant material. 'In particular, the material is often fed at a preset rate, and it is frequently difficult for the operator both to actuate feed of the material and to control the rate of feeding. It may further be noted in this connection that a particularly difficult :problem exists where a user desires with such prior apparatus to change from a first to a-second type of sealtant material which successive materials may also be of different rel. The barrel is readily interchangeable with other barrels in order to enable application of successive and possibly differing types of materials without intercontamination. An insulating sleeve covers the :barrel, which is furthermore joined to the motor casing and piston grip, through an insulating bushing. These insulating elements serve to minimize heat transfer from the normally quite hot barrel to surfaces likely to be contacted by the apparatus operator.

. BRIEF DESCRIPTION OF DRAWINGS The invention isdiagram'matically illustrated, by way of example, in thedrawings appended hereto, .in which:

FIG. I is a longitudinalcross-section through ahandheld extruding apparatus in accordance with the present invention;

FIG. 1A is a fragmentary cross-sectional detailof the contact arrangement at the interface of the barreland bushing portions of the FIG. 1 apparatus; FIG. 2 is a plan view of the FIG. 1 apparatus;

FIG. 3 is a front-end view of the FIG. 1 apparatus;

FIG. 4 is a transverse cross-section taken along the line 44 of FIG. 1, and depicts the external electrical connections towards the input end of the apparatus barrel;

FIG. 5 is a plan view taken along the broken line 5-5 of FIG. 1, and illustrates the external appearance of the circuit board and associated components present in the casing portion of the apparatus;

FIG. 6 is an elevational, partially sectioned view of' FIG. 10 is a simplified electrical schematic of the temperature control circuit utilized in the present apparatus.

DESCRIPTION OF PREFERRED, EMBODIMENT In FIG. 1 herein, a longitudinal cross-sectional view appears through a hand-held extruding apparatus in accordance with the present invention. In considering this Figure, simultaneous reference may usefully be had to FIG. 2, setting forth a plan view of the apparatus 20, and to FIG. 3 herein, depicting a front end view of the said apparatus. Referring particularly to FIG. 1, the apparatus 20 is seen to include a barrel 22, which isjoined at its input end to a casing 26 through a barrel bushing 46. The barrel 22 at its output end is joined to a cap 25, which cap is provided with a nozzle 24 adapted for dispensing the material extruded by the apparatus. Barrel 22 is covered externally by an insulating sleeve 44,

which is formed of an asbestos composition or other high temperature insulator. Similarly, bushing 46 is formed of a phenolic-based plastic or other material which is relatively insulating with respect to heat transfer and electrical conductivity. These two elements thus cover the bulk of the forward portions of apparatus 20, and, as will become increasingly apparent, serve to prevent transfer of heat from the relatively hot metallic barrel to the hands of an operator, and also minimize the danger of shock.

The casing 26 may be regarded as including a motor housing 28, a pistol-grip portion 32, and a gear train housing 30. A line power plug appears at 36, and when connected to an electrical outlet provides conventional AC line power for all motor and control functions in the apparatus. The trigger 34 at pistol-grip 32 provides for finger-tip control of the motor within housing 28. The several portions of casing 26 as have been described, are conventional and substantially correspond to commercially available structures of this type that are commonly used in hand-held electric drills or the like, the primary purpose of these several components being to provide motive power for controlled rotation of the material feed screw 50 (to be referred to hereinbelow), and also to provide connections for powering the heating elements and associated control circuit portion of the apparatus. In accordance with such known configurations, it will be evident to those skilled in the art that the motor of casing 26 may be appropriately regulated for a desired rotational rate in accordance with the requirements imposed on apparatus 20 in a given situation. Again, it is emphasized that the motive portion of the present apparatus is not per se of my invention, but rather of commercial design; accordingly no further details are set forth herein respecting the speed control or related aspects hereof.

Returning to FIG. 1, it is seen that a material feed passage 23 extends axially the length ofbarrel 22. The material feed screw 50 is mounted for rotation within the said passage 23; feed screw 50 thus terminates at a shank portion 52 which may be of square or other cross-section having planarfsides (such as polygonal),

. the shank being seated within a mating opening 51 provided at a driving gear 54. Driving gear 54, which is journaled within a bearing 56, is the final power transmitting member in the gear train present within gear train housing 30, and thus transmits power from the motive system present within motor housing 28. Material to be extruded by the present apparatus is fed through material feed opening 42 which passes through both bushing 46 and the barrel 22 which partially underlies the bushing at such axial point. The said material, which may comprise the polymeric compositions previously mentioned, is typically fed in rope form, and

upon contacting the feed screw 50 is advanced through passage 23 toward the output end of the device. The nozzle 24 through which such materials actually exit, is engaged with cap 25 by being threaded therein as at 27. Cap 25 in turn, as may best be seen in FIG. 3, is joined to barrel 22 by a pair of screws 58 and 60, which pass through the cap and into threaded portions 62, 64 (FIG. 7) of the passages 66 and 68 which are discussed further hereinbclow.

As may be seen, both from FIG. I and as well from the detailed barrel showings of FIGS. 6, 6A and 7, barrel 22 includes in addition to central feed passage 23, the pair of heating passages 66, 68 which passages extend parallel to feed passage 23 at off-axis positions which laterally flank the feed passage. The said heating passages 66 and 68, actually extend from that end of thebarrel' joining bushing 46, to the axial coordinate designated at 70 in FIG. 1, which point is close to the outpt end of the said barrel. These heating passages, as may be seen, for example, from FIG. 6A, are but slightly spaced from feed passage 23, and it will evident that heat provided within such passages may be readily transmitted to the extrudate passing through the feed passage. Heat is thus provided by a pair of elongated heating elements, one of which is seen at 72, which are positioned within the passages 66 and 68 and may typically extend from the terminal end 70 of such passages to a point such as 76, which is approximately at the axial point where material is fed into theapparatus. The said heating elements may typically compirse a refractory-bound heating element such as a so-called cal-rod" or other sturdy heating elements as are knwon in the art to be usefully and readily formed as cylindrical or similarly shaped elongated bodies.

As may bebest seen in both FIGS. 1 and 6, a fourth passage, parallel to the three passages previously discussed, is provided in the barrel 22. This latter element, the heat sensor passage 78, is seen in FIG. 6A to comprise a bore which is displaced from each of the heating passages 66 and 68 by about the circumference" of barrel 22. Passage 78 extends the complete length of barrel 22, and, as is best seen in FIG. 6, is in good thermal contact with feed passage 23 through the relatively thin wall 80. Passage 78 is closed at its end adjacent cap A I 25 by a ball bearing 82, which is press-fitted into the opening terminating the said passage at such point.

In accordance with an important aspect of the present invention, a heat sensor 84 is positioned within passage 78 at an axial point about 16. of the way from the feed opening 42 toward the output end of the barrel. The sensor 84 typically comprises a solid state thermistor, which, as will be hereinbelow set forth in greater detail, is disposed in a suitable control circuit with the heating elements. In accordancewith this aspect of the invention, an operator of the present device, by utilizing temperature selection knob 38 (FIG. 3) sets the pointer 41 of such knob at a desired reading on dial plate 39, whereupon the control circuit including sensor 84 and the heating elements acts to maintain the selected temperature in an accuratefashion within feed passage 23.

A key aspect of the present invention derives from the fact that the barrel 22, together with its associated cap 25 and nozzle 24, may be readilydisassembled and removed from the remaining portions of apparatus 20, whereupon a further differing barrel-cap-nozzle assembly (including the associated heating elements and heat sensor) may be substituted for the removed elements. The important advantageof such feature arises from the artisans requirement to often utilize different types of extruded materials for differing portions of a given job, or for successive jobs. For example, it may be advantageous, or even necessary, for such artisan to uti lizean extrudate of a first color in connection with a first portion of a job, and an extrudate of a second portion of the same job. In the past this has represented a v perplexing porblem, and one not readily solved, in that were one to use the same apparatus for application of both materials, the various passages, etc. associated with the first material would have to be initially cleaned, or, in the alternative a large amount of the second material would have to be wasted in an initial purging of the system. As the nozzle 24 is itself threaded into cap 25 at 27, one may, further, readily substitute nozzles of specific cross-sections or end shapes in accordance with the requirements of a given job. This latter feature also enables replacement of damaged nozzles in an expeditious manner an important consideration in that the nozzle is often the cheapest part of the nozzle-cap assembly.

Ignoring, for a moment, the various electrical connections made to the heatingelements and the heat sensor at-barrel 22, it will, firstly, be seen (from FIG. I) that the said barrel joins the remainder of apparatus through the heat insulating bushing 46 prevkously referred to. The bushing 46 is seen in greater detail in FIGS. 8, 9, 8A and 8B. The said bushing is thus seen to be provided with a threaded portion 86 which engages mating threads provided at 88 at the adjoining end of gear train housing 30. A key slot is provided at 89 transverse to the threaded portion 86; the set screw 48 passing through housing 30 (FIG. 2) engages with such slot upon being advanced, to lock the threaded bushing in place.

As best seen from the end view of FIG. 8B, bushing 46 is provided with a pair of threaded holes 90 and 92, angularly displaced 90 from one another; the axial position of the holes is evident from the depiction of hole 92 in FIG. 8. When barrel 22 is fully inserted into the bushing, as in the position set forth in FIG. 1, a pair of recesses 94 and 96 (FIGS. 68 and 7) will reside directly in line with the threaded holes 90 and 92. It may, in this connection, be noted that the entire barrel 22 is actually keyed for proper angular insertion into bushing 46,

by virtue of several projections 98, 100, 102 and 104 (FIG. 6B) which mate with corresponding longitudinally directed slots 106, 108, 110 and 112 formed in the interior walls of bushing 46 (FIG. 8B). The support handle 40 is provided at its end opposite the portion to be grasped, with a threaded portion which may be advanced within one or theother of the holes 90 and 92, so as to come to rest at one or another of the recesses 94 and 96, thereby locking the'barrel and bushing totrical connections) one may disengage and removea barrel then in use, by. merely unthreading the handle portion 40, removing the set screw (not shown) from the hole 90 or 9 2.intowhich it is threaded, and then pulling the barrel from its no-longer restrained position. One may, in fact, beassisted in removalof the barrel in this fashion by applying power to feed screw 50,

in that once the barrel is no longer fixedly held in place, rotation of the said screw (assuming a certain amount of extrudate remains in passage 23) will force the extrudate against the bounding portions of the barrel to thereby drive the barrel forward. It will further be appreciated that once the barrel 22 is so removed one may, if he so desires, thereupon directly removed feed screw 50, in that the latter is only retained at such time by means of the frictional engagement of shank portion 52 with the mating openingSl at driving gear 54.

We turn now to consideration of the manner in which electrical connections are made to the heating elements 72 and to the heat sensor 84, all such elements being, as previously discussed, positioned within barrel 22. Firstly, (referring to both FIGS. 1 and 1A) there is secured at the input end of the barrel 22 a plate 116, comprising insulating laminates or the like, the said plate being-provided with male electrical contacts as are appropriate to effect electrical connections to the heating elements, and to sensor 84. When the barrel is positioned in operative fashion within bushing 46 the various male contacts of plate 116 engage corresponding female socket contacts 114 in the bushing 46. Two

the corresponding female receptacle to the powering portion of the apparatusAs is best seen in the transverse cross-seetional view of FIG. 4, taken along the line 4-4 of FIG. 1, a series of electrical connections are thus provided. The various wires thus seen entering through appropriate passages in bushing 46 include a groundeonnection at 122, connections to the heating elements at 124,v 126 and at 128, 130, and a pair of connections 132, 134, to heat sensor 84.

As seen from the broken away portion of FIG. 1 and from simultaneous examination of FIG. 4, the various wires 136 leading from plug assembly 116, pass into the casing portion 26 of the apparatus, and into a male terminal 138 ofa connector 144. The connector is a commercially available element such as, for example, a component of this type available from Molex, Inc., and terminal 138 includes a chamfered edge 142 which enable secure mating of the terminal with a matching female terminal. The thus mated connector 144 is seen in FIG. 1 to include the male terminal 138 and female terminal 146. Various wire connections 148 lead downwardly in=casing 26 from connector 144 to one end of a similar connector 150, which in turn is connected at its opposite end to line power to thereby provide power input for the heating and control functions of apparatus As may now be seen from examination of the brokenaway portion of FIG. 1, and from simultaneous examination of the plan view of FIG. 5, taken along the broken line 5--5 of FIG. 1, an important advantage of the present invention arises by virtue of the fact that the entire heating control circuit of the apparatus is mounted upon a circuit board 154.

Circuit board 154 is supported from casing 26 by means of a stand-off 156. A pair of screws is threaded into the stand-off at opposite ends thereof, respectively passing through the adjacent wall of the casing and through the circuit board 154. The head of one such screw is seen at 158. The various electrical components forming part of the heating control circuit are shown externally in the plan view of FIG. 5. They will be discussed in terms of their electrical function in connection with the schematic diagram of FIG. however, certain external aspects of the mounting arrangement are apparent from FIG. 5, including, for example, the potentiometer 160 which is connected to the temperature selection knob 38 (previously discussed) through a rotatable shaft 164 passing through casing 26. Also to be noted is the indicator bulb 166 which is mounted toward the top of board 154, so that the tip thereof is visible through an opening 168 provided in casing 26, adjacent the temperature selection knob 38. The said indicator bulb provides a visual signal to the operator that heating of elements 74 and 76 is occurring. A triac 162, forming part of the heating control circuit, extends downwardly from the bottom of board 154. The central opening 163 therein is used for connecting the body of such device by means of a nylon screw 170 to the interior wall of casing 26. A thin mica insulation (not apparent on the scale of FIG. I) intervenes between triac 162 and casing 26.

It should be particularly noted in connection wit FIG. 5 that electrical connections to the heating control circuit mounted on the board, are effected through means of female terminal 146 at the upper end of FIG. 5, and through the male terminal 171 at the bottom of the figure. These two terminals connect respectively to connectors 144 and 150, previously discussed. It will be evident that one of the important advantages of the present'circuit arrangement is that in the event of a failare of one or more of the circuit components it becomes a relatively simple matter to effect repairs. In particular one may interrupt the connections to the board 154 at the pair of connectors 144 and 150, and thereupon, subsequent to loosening the several screws retaining the board in fixed contact with casing 26, remove the entire board structure and replace it with a new similar unit. Since the various solid state components incorporated in the control circuit are relatively inexpensive, this simple replacement operation is an economical one; it not only enables repair of apparatus 20 by relatively inexperienced personnel, but also from a time viewpoint expedites such repair and thereby prevents down-time in the comparatively much more expensive and valuable apparatus 20 in which the circuit board is incorporated.

Unlike numerous prior extruding apparatus of the general type to which the present invention pertains, the instant device is provided with a highly sensitive temperature control circuit, which in conjunction with the extended heating elements 74 and 76 previously discussed, and with the effectively positioned sensor 84, provides for most efficient control in heating of the extrudate passing through the apparatus. A simplified schematic diagram of a control circuit suitable for such purposes is shown on FIG. 10 herein. This circuit, of course, corresponds to that externally set forth in connection with FIG. 5.

As thus seen in FIG. 10, line power is provided to control circuit 174 at the pair of terminals 176, 178. The load, in the form of the heating elements is connected across output terminals 180, 182. The heat sensor 84, which as has been previously indicated as preferably a thermistor, is connected across the output terminals 184, 186. Flow of, electrical heating power to the load at terminals 180, 182 is controlled bymeans, of a triac 162 which is connected between one said ter-:

minal and one of the AC power lines. The heat-sensing thermistor, together with variable resistor .188 (corresponding to potentiometer form one side ofya bridge circuit, with the fixed resistors and 192 forming the other side. The variable resistor 188 is set by means of temperature selection knob 38 to the temperature level desired for the apparatus. When the bridge is unbalanced due to temperature changes detected at the thermistor a signal is provided to an integrated circuit zero voltage switch 194, to enable the latter, and thereby provide pulses via line 196 at line frequency rate to the gate circuit of triac 162 which, in turn, provides heating of the load. Resistor 198 is a biasing element, providing with variable resistor 188 an appropriate division of potential to yield appropriate potential levels for the associated inputs to switch 194. The AC input at terminal 178 is also seen to be applied through a dropping resistor 200 to the indicated bulb 166, previously discussed. When triac 162 is conducting, that is to say, when heating is actually being effected, it will be clear that the bulb 166 is also activated, providing a visual indication to the operator of apparatus 20.

The zero crossing switch 194 is a commercially available device well-known in the art, a suitable model for present purposes being, for example, available from Motorola Semi-Conductors under the designation MFC 8070. The detailed electrical circuit of the cited switch is set forth in specification sheets available from the manufacturer. Suffice for the present purposes to note that the integrated monolithic structure includes an internal voltage regulating section incorporating a zener diode, a threshold detector, a differential amplifier input stage for sensing the resistance bridge previously referred to, and an output driver stage for triggering triac 162. The several output terminals from switch 194 are identified in FIG. 10 by the numerical designations utilized by the manufacture. In terms of these designations: terminal No. 2 is an input to the differential amplifier stage of the said switch; terminal No.

3 provides a reference input to the same stage; terminal No. 4 is to the collectorof a pre-amplifying transistor; terminal No. 5 is to the ground side of the zero voltage detecting stage; and terminal No. 7 provides the pulse output from the output driver stage of switch 194. Terminals Nos. 6 and 8 are to the internal regulatory portion ofthe D.C. power supply for circuit 174. Capacitor 202 is a power supply capacitor cooperating with the diode regulators internal of switch 194; resistor 204 provides an appropriate drop in line potential.

While the present invention hasbeen particularly set forth in terms of specific embodiments thereof, it will be understood in view of the present disclosure, that numerous variations upon the invention are now enabled to those skilled in the art, which variations yet reside within the scope of the instant teaching. Accordingly, the invention is to be broadly construed, and limited only by the scope and spirit of the claims now appended hereto.

I claim: v

1. A hand-held extruding apparatus for applying thermoplastic sealant. materials to surfaces, comprising in combination: g I

a. a barrel having a material feed passage longitudinally'extending therethrough; n

i b. a feed screw mounted for rotation in said feed pas- Sage;

c. motor means mounted at said apparatus for driving said feed screwlin response to operator control thereof; v I

(1. said barrel having a plurality of heating element passageways extending parallel to said feedpassage;

e. rod-like heating element mounted in each of said passageways and extending therein for a substantial portion of the length of said feed passage;

, f. a heat sensor mounted in said barrel for sen sing the temperature in the vicinity of said feed passage; g. heating control circuit means connected to said .heater elements and said sensor means for applying power to said heating elements to maintain a preselected temperature in said barrel;

h. means for, feeding said material to said sage; and

i. orifice means at the output end of said feed passage for dispensing said material.

2. Apparatus according to claim 1 wherein said motor means is mounted at a piston-grip casing at the input end of said apparatus.

3. Apparatus in accordance with claim 2, including a heat and electrically insulating sleeve covering said barrel.

4. Apparatus in accordance with claim 3, wherein said barrel is joined to said casing through a heat and electrically insulating bushing.

5. Apparatus in accordance with claim 4, wherein said barrel is interchangeable.

6. Apparatus in accordance with claim 5, wherein said orifice means includes a cap and a nozzle removably secured to said cap, whereby said nozzle is readily interchangeable.

7. Apparatus in accordance with claim 5, wherein feed passaid bushing is thi eadingly engaged with said casing, and wherein said barrel is slidingly telescopeable within said bushing, said barrel being provided with a depression in the outer wall thereof and said bushing being provided with a threaded hole overlying said depression, a threaded member being insertable into said hole for engaging upon advancement with said depression to lock said bushing and barrel together.

8. Apparatus in accordance ,with claim 7, wherein said threaded member comprises the threaded end of an elongate handle for said apparatus.

9. Apparatus in accordance with claim 8, including a pair of said depressions and a pair of said holes, the members of each said pair beingangularly displaced from one another to alternate sides of the vertical plane of said apparatus, whereby said handle may be threaded into one or the other of said holes in accordance with the left or right-handedness characteristic of the apparatus operator; and a set screw being threadably insertable into the hole and depression not engaging said handle, for augmenting the said locking of said bushing and barrel. r

10. Apparatus in accordance with claim 9, wherein said motor is activated by a trigger switch at said pistol grip, and is speed-controllable.

11. Apparatus in accordance with claim 10, including electrical connection means at the input end of said barrel which are ,disengageable from said heating control circuit upon said barrel being slidout from said bushing. I, i 1 12. Apparatus in'accordance with claim 11, wherein said heating control circuit is formed on a circuit board, said board being removably mounted at said casing. r

13. Apparatus'in'accordance with claim 1, including a heat sensor passageway formed in said-barrel parallel to saidheating element passageways, said heat sensor comprising a thermistor positioned in said sensor passageway toward the output end of said apparatus.-

14-. Apparatus in accordancewith claim 13, wherein said heat controlcircuit comprises: a resistance bridge including at one side thereof said thermistorand a variable resistor setable in accordance with said preselected temperature, and at the other side thereof, a pair of reference resistors; a triac connected in series with said heating elements; and an integrated circuit zero crossing switch connected between said bridge output and said triac, for enabling said triac at line frequency in accordance with a signalprovided to said switch by unbalancing of said bridge, thereby providing ON-OFF control of said heating elements.

15. Apparatus in accordance with claim 14, including an indicator lamp connected to the output from said triac, in parallel with said heating elements, for providing a visual indication of heating of said elements.

16. Apparatus in accordance with claim 14, including a heat and electrically insulating sleeve covering said barrel, and wherein said barrel is removably joined to said casing through a heat and electrically insulating bushing.

i i i i i 

1. A hand-held extruding apparatus for applying thermoplastic sealant materials to surfaces, comprising in combination: a. a barrel having a material feed passage longitudinally extending therethrough; b. a feed screw mounted for rotation in said feed passage; c. motor means mounted at said apparatus for driving said feed screw in response to operator control thereof; d. said barrel having a plurality of heating element passageways extending parallel to said feed passage; e. rod-like heating element mounted in each of said passageways and extending therein for a substantial portion of the length of said feed passage; f. a heat sensor mounted in said barrel for sensing the temperature in the vicinity of said feed passage; g. heating control circuit means connected to said heater elements and said sensor means for applying power to said heating elements to maintain a preselected temperature in said barrel; h. means for feeding said material to said feed passage; and i. orifice means at the output end of said feed passage for dispensing said material.
 2. Apparatus according to claim 1 wherein said motor means is mounted at a piston-grip casing at the input end of said apparatus.
 3. Apparatus in accordance with claim 2, including a heat and electrically insulating sleeve covering said barrel.
 4. Apparatus in accordance with claim 3, wherein said barrel is joined to said casing through a heat and electrically insulating bushing.
 5. Apparatus in accordance with claim 4, wherein said barrel is interchangeable.
 6. Apparatus in accordance with claim 5, wherein said orifice meAns includes a cap and a nozzle removably secured to said cap, whereby said nozzle is readily interchangeable.
 7. Apparatus in accordance with claim 5, wherein said bushing is threadingly engaged with said casing, and wherein said barrel is slidingly telescopeable within said bushing, said barrel being provided with a depression in the outer wall thereof and said bushing being provided with a threaded hole overlying said depression, a threaded member being insertable into said hole for engaging upon advancement with said depression to lock said bushing and barrel together.
 8. Apparatus in accordance with claim 7, wherein said threaded member comprises the threaded end of an elongate handle for said apparatus.
 9. Apparatus in accordance with claim 8, including a pair of said depressions and a pair of said holes, the members of each said pair being angularly displaced from one another to alternate sides of the vertical plane of said apparatus, whereby said handle may be threaded into one or the other of said holes in accordance with the left or right-handedness characteristic of the apparatus operator; and a set screw being threadably insertable into the hole and depression not engaging said handle, for augmenting the said locking of said bushing and barrel.
 10. Apparatus in accordance with claim 9, wherein said motor is activated by a trigger switch at said pistol grip, and is speed-controllable.
 11. Apparatus in accordance with claim 10, including electrical connection means at the input end of said barrel which are disengageable from said heating control circuit upon said barrel being slid out from said bushing.
 12. Apparatus in accordance with claim 11, wherein said heating control circuit is formed on a circuit board, said board being removably mounted at said casing.
 13. Apparatus in accordance with claim 1, including a heat sensor passageway formed in said barrel parallel to said heating element passageways, said heat sensor comprising a thermistor positioned in said sensor passageway toward the output end of said apparatus.
 14. Apparatus in accordance with claim 13, wherein said heat control circuit comprises: a resistance bridge including at one side thereof said thermistor and a variable resistor setable in accordance with said preselected temperature, and at the other side thereof, a pair of reference resistors; a triac connected in series with said heating elements; and an integrated circuit zero crossing switch connected between said bridge output and said triac, for enabling said triac at line frequency in accordance with a signal provided to said switch by unbalancing of said bridge, thereby providing ON-OFF control of said heating elements.
 15. Apparatus in accordance with claim 14, including an indicator lamp connected to the output from said triac, in parallel with said heating elements, for providing a visual indication of heating of said elements.
 16. Apparatus in accordance with claim 14, including a heat and electrically insulating sleeve covering said barrel, and wherein said barrel is removably joined to said casing through a heat and electrically insulating bushing. 